Many lens manufacturing processes require applying a film onto a blank of the lens. The film is designed to provide the final lens with additional properties or functions that the lens blank itself does not have initially. Such properties or functions may be of optical type, for example anti-reflection function, mechanical type, including anti-scratch surface protection, antistatic, etc. This allows the lens blank and the film to be supplied from separate channels, and therefore improves the final yield of the lens production.
But lens production has stringent quality requirements. Indeed defects caused during applying the film onto the lens blank may impair the optical efficiency of the final lens, for example by producing light diffused by the defects. Larger defects may be wrinkles, tears or uneven stretches in the film, and also scratches on the film or the blank surface. All these defects may lead to discarding the lens produced, especially when the lens is intended for ophthalmic use, because aesthetic issues are then very important too.
Therefore, the processes which are implemented for applying a film structure onto a lens blank have been optimized for reducing the defects generated in the final lens. Such process involves the following steps:                /a/ arranging the film structure between a top face of the lens blank and a resilient cushion; and        /b/ pressing the film structure against the top face of the lens blank by moving the resilient cushion and the lens blank closer to each other, thereby deforming the resilient cushion and suppressing a gap existing initially between the film structure and the top face of the lens blank, with a contact area of the film structure with the top face which increases when the resilient cushion is being crushed.        
Such process is efficient in producing an even application of the film structure onto the lens blank when the top face of this latter is convex. But difficulties arise when the top face of the lens blank contains concave patterns, which extend below a local average height of the top face. Indeed, the resilient cushion fails to push the film structure in the concave pattern so that the film structure conforms tightly to the shape of the pattern. In addition, using a cushion which is either more or less resilient never results in obtaining a satisfactory conformation of the film structure within the concave pattern.
Therefore, an object of the present invention is to propose an improvement to the known application process just described, which improves the quality of the film application when a special type of concave pattern is present in the top face of the lens blank.